Question 1

How do you calculate beam deflection for a simply supported beam?

Accepted Answer

For a simply supported beam with a central point load P: maximum deflection δ = PL³/(48EI). For a uniformly distributed load w: δ = 5wL⁴/(384EI). Where L is beam span (m), E is modulus of elasticity (GPa), and I is second moment of area (m⁴). Per ACI 318, deflection limit is typically L/360 for live load.

Question 2

How do I calculate the concrete mix design per ACI 318?

Accepted Answer

ACI 318 concrete mix design steps: 1) Determine required strength f'cr = f'c + 1.34s or f'c + 2.33s - 500 (psi). 2) Select w/c ratio from durability table. 3) Estimate water content (180-190 kg/m³ for 20mm aggregate). 4) Calculate cement content = water / (w/c). 5) Determine aggregate proportions by weight. Use our Concrete Mix Design Calculator for instant ACI-compliant results.

Question 3

How do you calculate rebar quantity for a concrete slab?

Accepted Answer

Rebar quantity = (Slab area / Spacing) × Length + Overlap allowance (typically 40 bar diameters). For a 100m² slab with 200mm spacing: Number of bars = 100/0.2 = 500 bars each way. Weight = Number × Length × Unit weight (kg/m). Our Rebar Calculator handles all reinforcement scheduling automatically.

Question 4

What is the Terzaghi bearing capacity formula for soil?

Accepted Answer

Terzaghi's ultimate bearing capacity: qu = cNc + qNq + 0.5γBNγ (for strip footing), where c is cohesion (kPa), q is surcharge pressure (kPa), γ is soil unit weight (kN/m³), B is footing width (m), and Nc, Nq, Nγ are dimensionless bearing capacity factors based on friction angle φ.

Question 5

How do I calculate retaining wall stability?

Accepted Answer

Three stability checks are required: 1) Sliding: FoS = (μ × W_total) / (Active earth pressure) ≥ 1.5. 2) Overturning: FoS = (Stabilising moment) / (Overturning moment) ≥ 2.0. 3) Bearing: σ_max = W/B × (1 + 6e/B) ≤ allowable bearing capacity. Active earth pressure Ka = tan²(45° - φ/2) per Rankine theory.

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